With the development of social economy, the speeding-up of life pace and the increases of emotional impact, the incidence of depression increased year by year. Depression which is one main type of mood disorders, is a syndrome characterized by significant and long-lasting depressed mood. Its main symptoms are depressed mood, decreased interest, pessimism, retardation of thinking, lack of initiative, self-blame from sin, poor diet and sleep, worry of suffering from various diseases, feeling of multiple discomforts, and in severe cases, suicidal thoughts and behaviors may occur. Clinically, the treatment of depression mainly relies on Western medicines, however, they all have varying degrees of side effect and dependence, though they are effective to some extent.
Agomelatine is the first and the only melatonin 1, 2(MT1 MT2) receptors agonist developed by Servier (France), and it is also a serotonin 2c (5HT2c) receptor antagonist. It is mainly used for the treatment of the onset of depression. The unique mechanism of agomelatine is completely different from that of the antidepressants which are widely used at present, such as selective serotonin reuptake inhibitor (SSRI) and serotonin-noradrenaline reuptake inhibitor (SNRI): SSRI and SNRI antidepressants achieve their antidepressant effects through increasing the concentration of serotonin, but this also brings about various side effects, such as weight changes, sexual dysfunction, withdrawal syndrome, and the like. The molecular structure of agomelatine directly binds to the serotonin 2c (5HT2c) receptor in the neural postsynaptic membrane in order to exert its antidepressant efficacy without increasing the serotonin concentration in the synaptic cleft. This unique mechanism makes agomelatine exert its antidepressant efficacy rapidly and effectively together with avoiding side effects of the drug to a maximal extent.
Another unique target of agomelatine involves the melatonin receptor. MT1 and MT2 receptors are densely distributed on human suprachiasmatic nucleus, which is in charge of human sleeping rhythm. Agomelatine is an agonist of MT1 and MT2 receptors. Through its agonistic effect on MT1 and MT2 receptors, the sleeping quality of patients would be well improved, and the waking state of patients would be improved during the daytime. There is a mutually causal relationship between the quality of sleep and the outcome of depression. It is reported that problems of sleeping disorders exist in 80% of depression patients. The improvement of sleeping quality directly promotes the improvement of general clinical states of depression patients. A large number of clinical studies have confirmed that agomelatine have ideal long and short term efficacies. It rapidly achieves efficacy and significantly reduces the relapse and recrudescence rates in depression patients, and the safety is significantly better than that of SSRI and SNRI drugs. In addition, it significantly improves sleeping quality of patients and the waking state during daytime together with reliving the core symptom of depression. It is no doubt that the creation of agomelatine brings about a new option in the treatment of depression for doctors and patients.
Chemical name of agomelatine is N-[2-(7-methoxy-1-naphthyl)-ethyl]acetamide with the structural formula below:

Agomelatine has been reported in several documents. For example, agomelatine, the preparation and the therapeutic use thereof are described in European Patent Specification EP0447285. A new synthetic method, a new crystal form of agomelatine and the pharmaceutical composition thereof are described in Chinese Patent CN1680284. A new crystal form VI of agomelatine, the preparation method thereof and pharmaceutical composition containing thereof are described in Application No. 200810174918.2. Another synthetic route of agomelatine is described in EP0447285; J.M.C,1994,37,3231-3239.
As well known, compounds may be present in two or more crystalline states, which is a natural property of a substance. The molecules having the same structure are crystallized into different solid forms which are known as homogeneous polycrystalline. Different kinds of crystals have different lattice energy, thus they exhibit physical properties of excellent purity and well reproducible. Taking advantage of a different preparation method, the present invention obtained a novel crystal of agomelatine which is different from those reported in the prior art, and the present invention is completed by obtaining X-ray powder diffraction spectra.